1. Field of the Invention
The present invention relates to a transmitting and receiving system in which a plurality of remote controls transmit infrared rays, electromagnetic waves, supersonic waves or other energetic signals of the same frequency are transmitted simultaneously to a single receiver in the same place.
In general, when machines or apparatuses are controlled from a distant place, these machines or apparatuses are equipped with receivers, and associated remote controls have means to perform wired communication or wireless communication with the machines or apparatuses by using infrared rays, electromagnetic waves, supersonic waves or other energies.
Such a remote control comprises means to permit command data to be manually or automatically input, means to modulate a carrier wave with the command data and means to transmit the so modulated carrier wave to an associated machine or apparatus through a given communication link or channel.
The receiver of the associated machine or apparatus receives the signal bearing command data to demodulate it and derive the command data for working accordingly. 2. Description of Related Art
In a conventional remote control analogue signals are sampled and quantized to be converted to digital signals, which are given in the form of frames, each composed of 16 to 32 bits, and then control data thus provided are transmitted at regular intervals.
There is no problem of interference or cross talk if a single remote control is used. Even if a plurality of remote controls are used, there is no problem of interference or cross talk as long as each remote control is used at a different time.
Recently there has been an increasing demand for simultaneous use of two or more remote controls to control a single machine or apparatus in the same place. In this case it is most important to prevent any Interference or cross talk between signals transmitted from different remote controls.
Such interference or cross talk is most likely to appear, if some remote controls send simultaneously signals of the same frequency at the same intervals in the same place, and then the signals from the remote controls will be mixed at the receiver of the machine or apparatus. Command data received there cannot be correctly interpreted, thereby causing malfunctions in the machine or apparatus.
In an attempt to reduce such interference or cross talk a different frequency is allotted to each remote control (multifrequency system), or the single machine or apparatus on the receiving side polls a plurality of remote controls to determine which one will communicate with the machine or apparatus next (polling system).
Transmitting and receiving units required in such multi-frequency or polling system, however, are complicated in structure, large in size, and expensive.